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Microbial Fuel Cell and Wastewater Treatment
Tom Curtis and Colleagues
Newcastle University, UK
Northumbrian Water Ltd, UK
Inexorable Rise of Energy Use in The Water Industry
Inexorable Rise in Energy Prices
But there is Energy in Wastewater!
• Bomb Calorimetry
• Domestic wastewater contains
– 7.6 kJ/L
– 2000 kWh/ML
• Probably more..
Heidrich 2011
Electro-genesis
Electro-genesis
Anaerobic breakdown of complex wastes
Domestic wastewater treatment in methanogenic reactors
Works well in S. America
– No 1o sedimentation tank
– Little sludge
– Lots of methane
– Up to 600,000 people
• Key interlinked problems
– Temperature
– Stability
– Nutrients
UASB treating domestic wastewater in NE Brazil
-5.0E+05
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
4 8 15
Po
pu
lati
on
(ce
ll m
l-1)
Temperature (oC)
Methanogenic taxa dominance
MMB
MSC
MST
1.86
2.25
3.04
y = 1.5688e0.0442x R² = 0.9991
0
1
1
2
2
3
3
4
0 5 10 15 20
Spec
ific
rat
e (f
emto
mo
lsC
H4 c
ell-1
d
ay-1
)
Temperature (oC)
Specific methanogenic activity
specificmethanogenicrate
0.005
0.011
0.014
y = 0.0037e0.097x R² = 0.8154
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0 5 10 15 20
Spec
ific
rat
e (f
emto
mo
ls C
H4 c
ell-1
) day
-1)
Temperature (oC)
Specific hydrolytic activity
Specific hydrolysis rateExpon. (Specific hydrolysis rate)
a) Methane production versus time at all temperature; b) Methanogenic populations at all temperatures (the trend shows that the lower the temperature the higher the hydrogenotrophic:acetotrophic ratio – hydrogenotrophic methanogenesis is supported at low temperatures; c) Specific methanogenesis rates; d) specific hydrolysis rates; all images above describe anaerobic digestion of raw domestic wastewater at 4, 8 and 15oC.
A Microbial Fuel Cell
A MFC is a device that uses bacteria to oxidize organic matter and produce electricity. The bacteria (attached to the anode) produce electrons that travel to the cathode (current).
Proton Exchange membrane
load
Anode Cathode
bac
teri
a
Oxidation products
(CO2)
Fuel (wastes)
e-
e-
O2
H2O
H+
This is how a MFC works
Source: Liu et al., Environ. Sci. Technol., (2004)
H2
Cathode
CO2 e-
H+
e-
Bacteria
Anode
PEM
No oxygen in cathode chamber
PS
O2
Ref: Liu, Grot and Logan, Environ. Sci. Technol. (2005)
No oxygen in anode chamber
0.25 V needed (vs 1.8 V for water electrolysis)
A Microbial Electrolysis Cell
Anaerobic technologies for wastewater treatment
MFC MEC Anaerobic Digestion
Temperatures 7.5 – 45 oC 4.5 – 40 oC > 20 oC
Process control
limited possible limited
Retrofittable unlikely possible possible
Organic Load low- high low - high high
Why retrofitting is important
• Pie chart of your water bill
– 30% Water
– 40% Wastewater
– 30% Financing cost:
• 25 years for fixtures
• 50 years for concrete!
1980 1985 1990 1995 2000 2005 20100
20
40
60
80
100
Was
tew
ater
tre
atm
ent
rate
(%
)
Year
Urban wastewater
Urban domestic wastewater
Municipal Wastewater Treatment Rates In China
Most Research is Small Scale
Sampling port
Chamber filled
with solution
(b)
ANODE
(carbon paper) Cathode
4 cm
Catalyst
PEM (Nafion)
Diffusion layer: - Reduces water loss
- Increases CE due to reduced O2 transfer into anode chamber
Most Research is Small Scale
Sampling port
Chamber filled with solution (b)
ANODE
(carbon paper)
The PEM can be omitted, increasing power generation
Cathode
4 cm
Catalyst
Ammonia-gas treatment of anode increases power
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.2 0.4 0.6 0.8 1
Current density (mA cm-2
)
Ce
ll V
olta
ge
(V
)
0
500
1000
1500
2000
Po
we
r d
en
sity (
mW
m-2
)
V-Treated
V-UntreatedP-Treated
P-UntreatedPower = 1970 mW/m2 (acetate) = 115 W/m3
Where are the microbes in a Microbial Fuel Cell?
Thick biofilm on wastewater fed microbial fuel cell
• Microbes accept electrons from organic matter – Electron donors
• Microbes donate electrons to reducible chemicals – Electron Acceptors
• e.g. oxygen
• Iron (oxides)
• In MFC anode is an electron acceptor
• Microbe breath anode!
Maturing anode community increases current
Voltages are modest
• Anode – Acetate oxidation
• 2HCO-3 + 9 H+ + 8e- => CH3COO-
+4H2O – -0.300V
• Cathode – Oxygen reduction
• O2 + 4 H+ + 4 e- 2 H2O – 0.805V IN THEORY
– ~0.200V In practice
E’emf = 0.200-(-300)= 0.500V
Power is increasing year on year
• Power increasingly expressed / m3
• May also / m2
– Anode
– Cathode
– Membrane
Logan & Regan, 2006. Trends in Microbiology. 14, 512-518
Most Researchers “cheat”
• Use – Acetate or sucrose instead of wastewater
– Warm rooms instead of ambient
– High conductivity buffer instead of wastewater
– Expensive materials instead of cheap ones
– Short runs at small scale instead of long ones at large scale
Research Challenges in Newcastle
• Scale
• Materials
• Coulombic efficiency
• Length of operation
• Valorisation
• Retrofitability
Rozendaal TIB 2008
Tentative costs WWT: anaerobic and MEC look best.
System Product Capital costs
(Euros/kg
COD)
Product
Revenue
(Euros/kg
COD)
Net
Revenue
(Euros/kg
COD)
Activated
sludge
N/A 0.1 -0.3 -0.3
Anaerobic
Digestion
CH4 0.01 0.1 0.1
MFC Electricity 0.4 0.2 -0.2
MEC H2 0.4 0.6 0.2
Rozendaal TIB 2008
Table1:Cost-performanceratioforthedifferentmembranematerials.Costwaslinkedto
powerdensityandcoulombicefficiency.
Cost/£m-2
P/mWm-2
Cost/P£mW-1
CE/%
Cost/%CE/£m-2%-1
Energygenerated
overalifetimeof10
years/kWhm
-2
Totalincome
generatedover10
years/£
CP 105 24±0.02 4.4 68±11 1.5 2.1 0.17RH 1.5 14±2.2 0.11 63±8 0.02 1.2 0.10Nafion 506 29±2.6 17.5 71±12 7.1 2.5 0.20
ETFE 3 29±3.4 0.10 92±6 0.03 2.5 0.20PVDF 2 11±0.5 0.18 66±20 0.03 1 0.08
Materials: Evaluation on Cost vs Performance
Christgen 2013
Less Current From Complex Wastes
Hydrolysis the rate limiting
Distinct communities
MEC performance on real wastes
• Research remains sparse, energy recovery often not reported, widely variable.
Paper Substrate Reported Energy recovery
Ditzig 2007 Domestic wastewater < 1%
Wagner 2009 Swine wastewater 179%
Cusick 2011 Winery wastewater (acetate supplement)
If methane yield used “energy would exceed electrical input”
Escapa 2012 Domestic wastewater
“energy consumption comparable to aerobic treatments”
Jia 2012 Piggery wastewater Input electricity efficiency 124% - term not defined
Low Yields imply large energy losses: possible uncoupling
Figure 6a: Biomass yield under different loads, OCV and control
0.1k ohms 1k ohms 10k ohms 25k ohms 50k ohms OCV Control
Bio
ma
ss y
ield
(g
VS
S/g
CO
D r
ed
uce
d)
0.00
0.05
0.10
0.15
0.20
Katuri 2007
Losing energy in the food chain?
Polymers
Monomers
Electrons
Two: Seeds, temperatures + feeds
Arctic soils UK wastewater
Lise Øvreås
Temp and seed: little effect Feed: big effect
16
0
20
8
40
60
2040
06080
Coulombic efficiency (%)
Power density (mVm2)
COD removal (%)
acetate cold soil
acetate cold w w
acetate w arm soil
acetate w arm w w
w astew ater cold soil
w astew ater cold w w
w astew ater w arm soil
w astew ater w arm w w
C2
Electro-genesis
Electro-genesis
Anaerobic breakdown of complex wastes
Acetate diversity: not a subset of wastewater diversity
.
0
2
4
6
8
10
12
14
16
Acetate Wastewater
Lo
g e D
ive
rsit
y
Bigger Trials
Worst conditions
• Heath Robinson design
• Low load
• Low temperatures
• Cheap materials
Energy recovery – Encouraging
0.00
20.00
40.00
60.00
80.00
100.00
120.00
Inp
ut
en
erg
y re
cove
ry (
%)
May June July August September October November
Heidrich et al., 2012
It’s the first time I have analysed the up-to date data - it does seem to be reducing in performance as we move from the summer (water temperature of 15- 20°C) to the winter (6-10°C). But even if it levels at 50% over the winter – with better design I’m sure it could be brought up – the main thing is its still working. The decline could also be due to time in operation – membranes clogging etc.
First Successful “Large” Trial
• Previous known failures – Warm climates
– Low conductivity
• Californian Vineyard – The temperature was 30°C, there was no membrane
and competitors to methanogens used the hydrogen
• Australian Brewery – It used reverse osmosis water and therefore the
wastewater had excesively low conductivity
Future Research: short term
• Suck it and see!
• Building 4 replicate pilot plants
• Improved hydrogen retention
• Improved cathodes
Long term: modelling
Glucose
Propionate
Val/Butyrate
Acetate H2
CH4
AcidogenesisXsug
AcetogenesisXpro Xbv
MethanogenesisXace Xh2
CO2
MOX
MRed
current
ElectroactiveXeab
anode
Glucose
Propionate
Val/Butyrate
Acetate H2
CH4
AcidogenesisXsug
AcetogenesisXpro Xbv
MethanogenesisXace Xh2
CO2
MOX
MRed
current
ElectroactiveXeab
anode
EPSRC Frontier! Long term multi-scale modelling with individual based foundation P
iciorean
u, C
., Head
, I.M., K
aturi, K
.P., van Lo
osd
recht, M
.C.M
., Scott, K
. (2
00
7). A
com
pu
tation
al mo
del fo
r bio
film-b
ased m
icrob
ial fuels cells. W
ater R
esearch 4
1, 2
92
1-2
94
0
Examples of Important work by other groups
• Animal wastes
– Lars Angenent
• Nutrient Removal
– Wetsus
• Novel applications
– Bruce Logan
• Novel cathode processes
– Korneel Rabaey
Summary • Wastewater contains 4 x more energy than required to
treat it.
• MEC one possible solution – Process fundamentals are obscure – Most “practical research” is unrealistic
• Progress needs:
– Cheap materials – Realistic Trials – Fundamental investigation leading to – New generation of models
Recommended